Land #18899, update ysoserial viewstate tool

docs/metasploit-framework.wiki/Dot-Net-Deserialization.md

@@ -82,24 +82,41 @@ Generate a .NET deserialization payload that will execute an operating system
 command using the specified gadget chain and formatter.
 
 Available formatters:
-   * BinaryFormatter
-   * LosFormatter
-   * SoapFormatter
+  * BinaryFormatter
+  * LosFormatter
+  * SoapFormatter
 
 Available gadget chains:
-   * TextFormattingRunProperties
-   * TypeConfuseDelegate
-   * WindowsIdentity
-
-Example: ./dot_net.rb -c "net user msf msf /ADD" -f BinaryFormatter -g TextFormattingRunProperties
-
-Specific options:
-   -c, --command   <String>         The command to run
-   -f, --formatter <String>         The formatter to use (default: BinaryFormatter)
-   -g, --gadget    <String>         The gadget chain to use (default: TextFormattingRunProperties)
-   -o, --output    <String>         The output format to use (default: raw, see: --list-output-formats)
-       --list-output-formats        List available output formats, for use with --output
-   -h, --help                       Show this message
+  * ClaimsPrincipal
+  * DataSet
+  * DataSetTypeSpoof
+  * ObjectDataProvider
+  * TextFormattingRunProperties
+  * TypeConfuseDelegate
+  * WindowsIdentity
+
+Available HMAC algorithms: SHA1, HMACSHA256, HMACSHA384, HMACSHA512, MD5
+
+Examples:
+  ./dot_net.rb -c "net user msf msf /ADD" -f BinaryFormatter -g TypeConfuseDelegate -o base64
+  ./dot_net.rb -c "calc.exe" -f LosFormatter -g TextFormattingRunProperties \
+    --viewstate-validation-key deadbeef --viewstate-validation-algorithm SHA1
+
+General options:
+    -h, --help                       Show this message
+    -c, --command   <String>         The command to run
+    -f, --formatter <String>         The formatter to use (default: BinaryFormatter)
+    -g, --gadget    <String>         The gadget chain to use (default: TextFormattingRunProperties)
+    -o, --output    <String>         The output format to use (default: raw, see: --list-output-formats)
+        --list-output-formats        List available output formats, for use with --output
+
+ViewState related options:
+        --viewstate-generator             <String>
+                                     The ViewState generator string to use
+        --viewstate-validation-algorithm  <String>
+                                     The validation algorithm (default: SHA1, see: Available HMAC algorithms)
+        --viewstate-validation-key        <HexString>
+                                     The validationKey from the web.config file
 ```
 
 The `-g` / `--gadget` option maps to the *gadget_chain* argument for the

lib/msf/core/exploit/view_state.rb

@@ -51,60 +51,29 @@ def generate_viewstate_payload(cmd, extra: '', algo: 'sha1', key: '')
   end
 
   def generate_viewstate(data, extra: '', algo: 'sha1', key: '')
-    # Generate ViewState HMAC from known values and validation key
-    hmac = generate_viewstate_hmac(data + extra, algo: algo, key: key)
-
-    # Append HMAC to provided data and Base64-encode the whole shebang
-    Rex::Text.encode_base64(data + hmac)
+    Rex::Exploit::ViewState.generate_viewstate(data, extra: extra, algo: algo, key: key)
   end
 
   def generate_viewstate_hmac(data, algo: 'sha1', key: '')
-    OpenSSL::HMAC.digest(algo, key, data)
+    Rex::Exploit::ViewState.generate_viewstate_hmac(data, algo: algo, key: key)
   end
 
   def decode_viewstate(encoded_viewstate, algo: 'sha1')
-    viewstate = Rex::Text.decode_base64(encoded_viewstate)
-
-    unless Rex::Text.encode_base64(viewstate) == encoded_viewstate
-      vprint_error('Could not decode ViewState')
-      return { data: nil, hmac: nil }
-    end
-
-    hmac_len = generate_viewstate_hmac('', algo: algo).length
-
-    if (data = viewstate[0...-hmac_len]).empty?
-      vprint_error('Could not parse ViewState data')
-      data = nil
-    end
-
-    unless (hmac = viewstate[-hmac_len..-1])
-      vprint_error('Could not parse ViewState HMAC')
-    end
-
-    { data: data, hmac: hmac }
+    decoded = Rex::Exploit::ViewState.decode_viewstate(encoded_viewstate, algo: algo)
+
+    vprint_error('Could not parse ViewState data') unless decoded[:data].present?
+    vprint_error('Could not parse ViewState HMAC') unless decoded[:hmac].present?
+    decoded
+  rescue Rex::Exploit::ViewState::Error => error
+    vprint_error("#{error.class.name}: #{error.message}")
+    return { data: nil, hmac: nil }
   end
 
   def can_sign_viewstate?(encoded_viewstate, extra: '', algo: 'sha1', key: '')
-    viewstate = decode_viewstate(encoded_viewstate)
-
-    unless viewstate[:data]
-      vprint_error('Could not retrieve ViewState data')
-      return false
-    end
-
-    unless (their_hmac = viewstate[:hmac])
-      vprint_error('Could not retrieve ViewState HMAC')
-      return false
-    end
-
-    our_hmac = generate_viewstate_hmac(
-      viewstate[:data] + extra,
-      algo: algo,
-      key: key
-    )
-
-    # Do we have what it takes?
-    our_hmac == their_hmac
+    Rex::Exploit::ViewState.can_sign_viewstate?(encoded_viewstate, extra: extra, algo: algo, key: key)
+  rescue Rex::Exploit::ViewState::Error => error
+    vprint_error("#{error.class.name}: #{error.message}")
+    return false
   end
 
   # Extract __VIEWSTATE from HTML

lib/rex/exploit/view_state.rb

@@ -0,0 +1,68 @@
+# -*- coding: binary -*-
+
+module Rex
+  module Exploit
+    class ViewState
+      class Error < Rex::RuntimeError
+      end
+
+      def self.decode_viewstate(encoded_viewstate, algo: 'sha1')
+        viewstate = Rex::Text.decode_base64(encoded_viewstate)
+
+        unless Rex::Text.encode_base64(viewstate) == encoded_viewstate
+          raise Error.new('Could not decode ViewState')
+        end
+
+        hmac_len = OpenSSL::Digest.new(algo).digest_length
+
+        if (data = viewstate[0...-hmac_len]).empty?
+          data = nil
+        end
+
+        hmac = viewstate[-hmac_len..-1]
+        unless hmac&.length == hmac_len
+          raise Error.new('Could not decode ViewState')
+        end
+
+        { data: data, hmac: hmac }
+      end
+
+      def self.generate_viewstate(data, extra: '', algo: 'sha1', key: '')
+        # Generate ViewState HMAC from known values and validation key
+        hmac = generate_viewstate_hmac(data + extra, algo: algo, key: key)
+
+        # Append HMAC to provided data and Base64-encode the whole shebang
+        Rex::Text.encode_base64(data + hmac)
+      end
+
+      def self.generate_viewstate_hmac(data, algo: 'sha1', key: '')
+        OpenSSL::HMAC.digest(algo, key, data)
+      end
+
+      def self.is_viewstate_valid?(encoded_viewstate, extra: '', algo: 'sha1', key: '')
+        viewstate = decode_viewstate(encoded_viewstate)
+
+        unless viewstate[:data]
+          raise Error.new('Could not retrieve ViewState data')
+        end
+
+        unless (their_hmac = viewstate[:hmac])
+          raise Error.new('Could not retrieve ViewState HMAC')
+        end
+
+        our_hmac = generate_viewstate_hmac(
+          viewstate[:data] + extra,
+          algo: algo,
+          key: key
+        )
+
+        # Do we have what it takes?
+        our_hmac == their_hmac
+      end
+
+      class << self
+        alias_method :can_sign_viewstate?, :is_viewstate_valid?
+      end
+    end
+  end
+end

spec/lib/rex/exploit/view_state_spec.rb

@@ -0,0 +1,67 @@
+require 'spec_helper'
+require 'rex/version'
+
+require 'rex/text'
+
+# rubocop:disable Lint/DeprecatedGemVersion
+RSpec.describe Rex::Exploit::ViewState do
+  let(:data) { Random.new.bytes(rand(10..100)) }
+  let(:key) { Random.new.bytes(20) }
+
+  context 'when the algorithm is SHA-1' do
+    let(:algo) { 'sha1' }
+
+    describe '.decode_viewstate' do
+      let(:encoded) { described_class.generate_viewstate(data, algo: algo, key: key) }
+
+      it 'returns the data and HMAC' do
+        decoded = described_class.decode_viewstate(encoded, algo: algo)
+        expect(decoded).to be_a Hash
+        expect(decoded[:data]).to eq data
+        expect(decoded[:hmac]).to eq described_class.generate_viewstate_hmac(data, algo: algo, key: key)
+      end
+    end
+
+    describe '.generate_viewstate' do
+      it 'generates the HMAC signature' do
+        expect(described_class).to receive(:generate_viewstate_hmac).with(data, algo: algo, key: key).and_call_original
+        described_class.generate_viewstate(data, algo: algo, key: key)
+      end
+
+      it 'generates a Base64 encoded blob' do
+        viewstate = described_class.generate_viewstate(data, algo: algo, key: key)
+        debase64ed = Rex::Text.decode_base64(viewstate)
+        expect(debase64ed).to eq data + described_class.generate_viewstate_hmac(data, algo: algo, key: key)
+      end
+    end
+
+    describe '.generate_viewstate_hmac' do
+      it 'delegates to OpenSSL::HMAC' do
+        expect(OpenSSL::HMAC).to receive(:digest).with(algo, key,data)
+        described_class.generate_viewstate_hmac(data, algo: algo, key: key)
+      end
+
+      it 'generates a 20 byte HMAC' do
+        hmac = described_class.generate_viewstate_hmac(data, algo: algo, key: key)
+        expect(hmac.bytesize).to eq 20
+      end
+    end
+
+    describe '.is_viewstate_valid?' do
+      let(:encoded) { described_class.generate_viewstate(data, algo: algo, key: key) }
+
+      it 'raises an Error when it can not be decoded' do
+        # use key.length / 2 to guarantee there is not enough data for the key to be found
+        expect { described_class.is_viewstate_valid?(Rex::Text.encode_base64('A' * (key.length / 2))) }.to raise_error(described_class::Error)
+      end
+
+      it 'returns true for the correct key' do
+        expect(described_class.is_viewstate_valid?(encoded, algo: algo, key: key)).to be_truthy
+      end
+
+      it 'returns false for the incorrect key' do
+        expect(described_class.is_viewstate_valid?(encoded, algo: algo, key: key + '#')).to be_falsey
+      end
+    end
+  end
+end